This invention relates to friction braking systems and more particularly to aircraft friction disc brakes having reinforced peripheral slots for use in multiple disc brakes.
In brake assemblies which employ a plurality of brake discs alternately splined to the wheel and axle of an aircraft, it is important to provide specially constructed drive means to reinforce the peripheral slots in the discs to relieve the severe stressing that otherwise would rapidly deteriorate the periphery of the discs. When disc brakes were constructed of steel, the discs were able to withstand the shearing and compressive forces exerted thereon between the slots and the torque transmitting members because of their physical properties. With the replacement of the steel discs with carbon composition discs which have better braking and heat sink characteristics it was important to provide reinforcing inserts at the peripheral slots of the discs since the carbon composites have less strength than steel. The problem with the use of metallic inserts is that the inserts transmit the forces directly to the carbon discs, which are subject to cracking or crumbling if the forces are not properly dispersed.
In some structures the load forces are transmitted via radially disposed pins to the carbon discs. These discs require precise machining for the placement of the radially located holes while simultaneously weakening the discs due to the removal of substantial material along the entire radial wall. In some structures the inserts for the peripheral reinforced slots transmit the forces to the insert rivets and then to the openings in the disc through which the rivets extend. These openings accept all of the discs loading and are therefore subject to undesirable very high stress concentrations. The present invention utilizes an insert at the peripheral slots that provides bearing surface in the drive notch or the peripheral slot of the carbon rotor or carbon stator, thus reducing the carbon area of loading resulting from the limited engagement of the mating wheel or torque plate driving lug with the slot and thereby extend the service life of the slot to equal that of the carbon composite's life as a heat sink. The insert has a pair of opposed faces which frictionally contact the opposite walls of the slots to distribute the load. Retaining clips or plates are used to retain the inserts in position within the slots and through its load distribution prevents fraying of the carbon composite heat sink material while also taking up stresses. The structure of the insert and clip provides for a large bearing area and minimizes the weight required to obtain the strength to handle the side loads due to misalignment. The construction permits the insert to float within the slot of the carbon disc. Such construction permits the partial absorption of the energy by the clip from the resulting movement of the insert. To further enhance this feature, the clip retainers are made of a spring type material. The present invention of the clip and insert simplify the machining, forgeability and lower weight. One feature of the present design which has proven highly desirable is the fact that the clip and insert combination removes the point or location of fatigue failure experienced in current designs while reducing the destructive natural frequencies of vibration by adding multiple contact interfaces which tend to reduce or disrupt the high frequency vibrations.